Methods for ligand exchange

Nanoparticles are usually obtained as organic-inorganic hybrids from wet-chemical syntheses, comprising of an inorganic core and a shell of organic capping ligands. The capping ligands are indispensable in the synthesis because they maintain the colloidal dispersity of nanoparticles and regulate the crystal growth into different shapes. It is difficult to obtain nanoparticles with designable shapes and surface properties directly from the synthesis. Ligand exchange opens a way to highly customizable surface properties of nanoparticles. As a result, the surface charge, functionality, accessibility of the surface sites by external molecules, dispersity and thus processability of the nanoparticles in different types of solvents, and charge transport properties across the nanoparticle assemblies, could be effectively tuned, which significantly broadens the application of the nanoparticles in different fields. This article summarizes the typical methods and mechanisms for the ligand exchange of nanoparticles that have been developed so far. In particular, ligand exchange strategies for phase transfer and clean surfaces of nanoparticles are extensively discussed. At the end, we provide a summary and some perspectives on the future development of the ligand exchange technology.